The Organic Light Emitting Diode (OLED) is a flat panel display technology which has great prospects for development. It does not only possess extremely excellent display performance but also properties of self-illumination, simple structure, ultra thin, fast response speed, wide view angle, low power consumption and capability of realizing flexible display, and therefore is considered as “dream display”. It has been favored by respective big display makers and has become the main selection of the third generation display element.
An OLED display generally comprises a substrate, an anode located on the substrate, an organic emitting layer located on the anodes, an electron transport layer located on the organic emitting layer, and a cathode located on the electron transport layer. As working, the Hole from the anode and the Electron from the cathode are injected to the organic emitting layer, these electrons and holes are combined to generate excited electron-hole pairs, and the excited electron-hole pairs are converted from the excited state to the ground state for achieving illumination.
The OLED can be categorized as Passive matrix OLED (PMOLED) and (Active matrix OLED) AMOLED according to their driving types. The power consumption of the PMOLED is high, and thus, it hinders the application in large scale display devices. Besides, in PMOLED, the aperture ratio is decreased along with the amount increase of the wirings. Therefore, the PMOLED is generally applied for the small scale display devices. The lighting efficiency of the AMOLED is high, and therefore, it is generally utilized for the large scale display devices of high resolution.
On the other hand, the AMOLEDs can be categorized into bottom emitting AMOLED display devices and top emitting AMOLED display devices according to the emitting direction of the light from the organic emitting layer.
Please refer to FIG. 1. FIG. 1 is a sectional diagram of a bottom emitting AMOLED display device according to prior art. As shown in FIG. 1, the AMOLED display device comprises a first substrate 10 and a second substrate 20, which are separated and oppositely faced. A plurality of thin film transistors T and a plurality of first electrodes 31 are formed on an inner surface of the first substrate 10, wherein each first electrode 31 is connected to one thin film transistor T, and an organic layer 32 is formed on the first electrodes 31 and the thin film transistors T, and second electrodes 33 are formed on the organic layer 32. The organic layer 32 in one pixel P emits lights of three colors: red light R, green light G and blue light B. The AMOLED display device further comprises: a dryer 21 formed on the inner surface of the second substrate 20, and employed to remove the water and the air which possibly invade in the spaced room between the first, the second substrates 10, 20. The seal 12 is formed between the first, the second substrates 10, 20, and surrounds elements like, the first, the second electrodes 31, 33, the organic layer 32, the thin film transistors T for protecting the aforesaid elements away from the foreign water and the air.
In the bottom emitting AMOLED display device shown in FIG. 1, the light emits passing through the bottom where the thin film transistors are formed, and it has descended aperture ratio by being compared with the top emitting AMOLED display device. On the other hands, the top emitting AMOLED display device possesses higher aperture ratio but the cathode is generally built on the organic layer. The selection of the material for manufacturing the cathode is restricted. Thus, the transmittance is restricted and display effect is degraded.